The present invention relates to an apparatus for automatically adjusting offset correction values for current detectors in a digital controller for a servo motor for use in a high precision NC system, robot, etc.
Heretofore, in a digital control apparatus for a servo motor for use in a high precision NC system, robot, etc., in the case where a current detector composed of an analog circuit is used as current detecting means, correction of an offset of an output of the current detector is carried out. That is, when turning on a power source, an output voltage of the current detector, which is detected while the servo motor is stopped, is set as an offset correction value, and the offset correction value which has been set upon turning on the power source is not updated while the motor is in operation.
However, in the above-mentioned prior art apparatus, there arises a problem that, when an error occurs between an actual offset value and the offset correction value, which has been set when turning on the power source, due to a change of an ambient temperature, a temperature rise in component elements of the current detector and the like while operating the servo motor for a long period of time, a ripple having the same period as that of an electrical angle is generated in the torque of the servo motor.